Hard to watch, impossible to forget. That’s Beasts of No Nation, a grueling war story set in an unnamed African country. Idris Elba gives a powerhouse performance as the commandant, the warlord of a rebel army that trains children as soldiers. His new recruit is Agu (Ghanaian discovery Abraham Attah), a boy who saw his family slaughtered. His army indoctrination includes heroin (“brown-brown”), sexual abuse and killing with a machete.

In adapting the novel by Nigerian-American author Uzodinma Iweala, writer-director Cary Joji Fukunaga (True Detective, Season One) is unsparing in treating this timely, terrifying subject. Elba (The Wire, Luther) gives the commandant a lethal swagger and inklings of a buried conscience that make his brutality even scarier. The Oscar for Best Supporting Actor should have his name on it. But it’s the remarkable Attah, whose young face reflects a hellish journey, that makes this fierce movie a blazing, indelible achievement.